This invention relates to an endoscope apparatus, more specifically to an endoscope apparatus with a reduced halation, a large observation area, and without an illumination nonuniformity.
An endoscope has been used in a broad number of fields, including the medical field to observe and diagnose the intra-corporeal of a human being. In addition, an endoscope has been used extensively, in the industrial field since a condition inside a machine can be observed and inspected without any endoscope interference.
An endoscope includes an object optical system for observing the intra-corporeal of a human beings and the interior of a machine, and an illumination optical system for illuminating an observation object. An illumination optical system consists of a light guide for transmitting the light from a light source to the tip end of the endoscope, and an illumination lens for extending a light distribution.
Moreover, it is well known to replace an illumination lens with frosted glass having a diffusion effect on supplied light. For example, FIG. 29(a) shows an illumination optical system which has a light guide 51 and a frosted glass 52, whereas FIG. 29(b) shows an illumination optical system which has a light guide 51 and an illumination lens 53.
In an endoscope observation, when an object having an intricate structure located inside a machine is observed, the brightness of the object within a visual field varies extremely due in part to the difference distances from the object, or the differences in the objective reflecting rate. When the dynamic range of the image pick-up element of an object optical system is not able to permit a certain brightness ratio, a part of the monitor screen might become white (hereinafter referred to as xe2x80x9chalationxe2x80x9d), which may interfere the observation.
A halation arises in the following cases: where illumination light is turned into direct reflected light by an object with a high reflecting rate, and the strong direct reflected light is then irradiated back into the object optical system; where an extreme illumination nonuniformity is generated when the illumination optical system at an end of the endoscope gets close to the object; and where both the above phenomena occur simultaneously.
In the medical field, a halation notably occurs when the object is pipe shaped, has multiple pleats is accompanied by waviness, for example, the large intestines.
That is, as shown in FIG. 30, when the endoscope end 55 is inserted in a pipe 54 with waviness and a waviness part 57, the pipe 54 exists close to an illumination optical system 56. The illumination light generated from the illumination optical system 56 is reflected on the waviness part 57 thereby generating a halation due to an extreme illumination nonuniformity. The wider the observation range of an object optical system is, that is, the larger the viewing angle a wide-angle object optical system has, the more often a halation will be generated.
The reason for the above is that, when an inner wall of a pipe and an endoscope get closer, in other words, when an illumination optical system and a range which performs a direct reflection (for example, a pleat of the large intestine) become close, strong reflected light is generated. The wider the angle object optical system has, the easier the reflected light irradiates into a visual field.
In an endoscope which has a wide-angle object optical system, a technique for preventing a halation, is described Japanese Patent Laid-Open Publication No. Hei 10-288742. The patent discloses an endoscope having an object optical system which can observe in a longitudinal direction as well as through a side of an endoscope simultaneously, by a illumination means illuminating the side. The diffusion means as the illumination means is indicated in FIG. 31, where FIG. 31(a) is a horizontal sectional view of the end part visual field of an endoscope, and FIG. 31 (b) shows the vertical sectional view thereof.
In FIG. 31(a), an object optical system 59 is provided such that it may exist in the center of an end part 58 of the endoscope. An optical axis of the radiation end of a light guide 60 which constitutes a front illumination optical system is arranged to be approximately parallel to the optical axis of the object optical system 59 so that the light side 60 illuminates a front visual field. The object optical system 59 has light guides 61 and 62 which constitute side illumination optical systems which illuminate side visual fields, respectively. Moreover, a frosted glass 63 is provided at the end of each the light guides 61 and 62 of the side illumination optical systems.
With this structure, since the illumination light in the pipe inner wall surface can irradiate uniformly even when the diffusion effect of an illumination light becomes high and it observes the pipe of a narrow diameter, the halation by the illumination light is seldom generated. Thus, in the Japanese Patent Laid-Open Publication No. Hei 10-288742, the frosted glass is provided at the end of the light guide which is a side illumination optical system so that the frosted glass is made to permeate the illumination light radiated from a light guide, thereby preventing halation by creating a diffusion effect.
However, in the case of simply arranging the frosted glass 63, as a diffusion plate, at the end of each of the light guides 61, 62, the light distribution range of the illumination light was narrow compared with that of the emitted light of an illumination optical system having a lens, so that it was easy to produce an illumination nonuniformity in a periphery of the visual field, and the periphery of the visual field became dark and was inadequate for observation.
Moreover, the illumination light distribution can be made wider only with illumination lenses, such as a concave lens. However, since the illumination light was not uniform, a halation occurred.
In view of the foregoing disadvantages inherent in the known prior art systems, the present invention solves the above-mentioned problems. Thus, it is an object of the present invention to provide an endoscope apparatus which can eliminate illumination nonuniformity and reduce halations so as to enable the endoscope apparatus to observe a wider range of an object.
In order to achieve the aforementioned objects, in a first aspect of the present invention, in an endoscope apparatus without an illumination nonuniformity, with a reduced halation and an observable large area, an end of the insertion part of an endoscope comprises a wide-angle object optical system, with two or more types of illumination optical systems having different illumination strength and light distribution. When illuminating the visual field range the illumination optical system having the greater illumination strength or light distribution among the illumination optical systems is arranged in the end position of the endoscope at both the sides of a long side of a screen of the wide-angle object optical system. At both of the sides of a short side of the screen of the wide-angle object optical system, the illumination optical system having a smaller illumination strength or a narrow light distribution is arranged among the illumination optical systems.
It is preferable that the illumination optical system consists of four illumination lenses.
It is desirable that the illumination optical system consists of a lens system which has a power and a diffusion element arranged at the object side. The lens system which has a negative power comprises a concave lens system which has a negative power and a diffusion element arranged at the object side.
It is also desirable that the lens system which has a power comprises a convex lens system which has a positive power, and a diffusion element arranged at the object side.
It is preferable that the effective area of the radiation surface of the diffusion element is larger than the effective area of the plane of incidence of the lens system.
It is desirable that the end of an endoscope have a streamline shape and an object optical system, and consists of a lens system which has a power in the direction of a slope of the streamline shape, and a diffusion element arranged at the radiation side wherein, the following conditions are fulfilled:
1 less than Ss/Si less than 8xe2x80x83xe2x80x83(1)
xcex8p less than xcex8i less than xcex8oxe2x88x92xcex8pxe2x80x83xe2x80x83(2)
wherein Ss is the effective area of the radiation surface of the diffusion element;
Si is the effective area of the plane of incidence of the illumination lens system;
xcex8p is the angle between the optical axes of the object optical system and the illumination optical system;
xcex8i is a half-angle of the light distribution angle of the emitted light from the illumination optical system; and
xcex8o is a half-angle of view of the object optical system.
In a second aspect of the endoscope apparatus without an illumination nonuniformity, with a reduced halation and an observable large area comprising a wide-angle object optical system, when illuminating the visual field range the illumination optical system having the greater light distribution and illumination strength is arranged among the illumination optical systems at the end position of endoscope corresponding to both sides of a long side of a screen of the wide-angle object optical system.
At the end position of the endoscope corresponding to both sides of the direction of a short side of the screen of the wide-angle object optical system, the illumination optical system having a narrow light distribution and small illumination strength is arranged among the illumination optical systems.
The illumination optical system consists of four illumination lenses.
The illumination optical system consists of a lens system which has a power, and a diffusion element arranged at the object side.
The illumination optical system consists of a concave lens system which has a negative power, and a diffusion element arranged at the object side.
The illumination optical system consists of a convex lens system which has a positive power and a diffusion element arranged at the object side.
The effective area of the radiation surface of the diffusion element is larger than the effective area of the plane of incidence of the lens system.
The end of the endoscope has a streamline shape and an object optical system, and comprises a lens system which has a power in the direction of a slope of the streamline shape, and a diffusion element configured at the radiation side wherein, the following conditions are fulfilled:
1 less than Ss/Si less than 8xe2x80x83xe2x80x83(1)
xcex8p less than xcex8i less than xcex8oxe2x88x92xcex8pxe2x80x83xe2x80x83(2)
wherein Ss is the effective area of the radiation surface of the diffusion element;
Si is the effective area of the plane of incidence of the illumination lens system;
xcex8p is a angle between the optical axes of the object optical system and the illumination optical system;
xcex8i is a half-angle of the light distribution angle of the emitted light from the illumination optical system; and
xcex8o is a half-angle of view of the object optical system.